(1) Field of the Invention
This invention relates to an improved unit for removing nitrates from household drinking water.
(2) Related Art
Nitrates typically enter household well-water streams as the result of runoff from agricultural operations using nitrate-based fertilizers, which leach into the ground water. Where not removed from the water stream, such nitrates can be very dangerous and even fatal, particularly to infants.
It is known to remove nitrates from water by adsorption of the nitrates on a bed of resin beads contained in a tank through which all the household water is passed. Known nitrate adsorption units typically comprise a tank containing the adsorbing resin, a regenerant tank containing a brine regenerant solution, and control and valving apparatus for periodically regenerating the resin. The control and valving apparatus periodically causes the brine to flow through the resin bed, removing the adsorbed nitrates therefrom. It is also known to regenerate the resin at varying intervals dependent on the amount of water passed therethrough, and on the amount of nitrates in the water, that is, on a demand basis. After regeneration, the nitrate-laden brine solution is then discarded in a drain.
Typical regeneration sequences include a backflush step, in which water flows through the resin in the opposite direction from normal flow, followed by a brining step, in which a brine solution flows through the resin in the "normal" direction. Subsequently the resin can be rinsed by further water flow in the "normal" direction. It is known to control performance of such sequences of steps automatically in response to a determination that regeneration is required.
Typical prior designs for nitrate removal units include a vertical cylindrical tank, formed of fiberglass, containing a bed of the nitrate-removing resins. Water enters the tank through one or more inlet openings located in an annular pattern around the top of the tank. The water flows downwardly through the resin and exits through a dip tube having a perforated distributor disposed in the lower portion of the tank. The dip tube extends up the center of the tank and exits through its center. Typically, a quantity of gravel is disposed around the distributor at the bottom of the dip tube. The gravel prevents the neutralizing resins from being withdrawn via the dip tube during normal use.
In a typical backflush operation, water is forced down the dip tube, out through the distributor at the bottom of the tank, and returns upwardly through the gravel and the nitrate-removing resin. This "fluffs up" the resin, ensuring that it is all exposed to the incoming water stream and is thus efficiently used. After backflush, brine is supplied via the annular inlet opening(s) and flows downwardly through the resin and up through the dip tube, thus following the "normal" water flow path. The brine removes the adsorbed nitrates from the resin bed, regenerating it. The nitrate-laden brine is discarded in a drain. The resin bed is then rinsed by the incoming water, facilitating return to normal service.
One deficiency with such conventional systems is that if iron is present in the water stream, even at low levels, the iron tends to deteriorate the resin material of the bed, preventing it to some extent from adsorbing the nitrates. Accordingly, even very low levels of iron in the water stream require a separate iron removal device prior to the nitrate-adsorbing equipment. It would be preferable if at least low levels of iron could be tolerated without the necessity of use of this additional piece of equipment, thus simplifying water treatment in these cases. At the same time it is desired to improve the efficiency of use of the nitrate-adsorbent resin.